This invention relates to compositions and methods for stabilizing subterranean clayey formations surrounding a borehole. More specifically, it pertains to clay stabilizing additives for aqueous fluids used in drilling, completing and maintaining boreholes.
When geological formations containing water swelling clays come in contact with water, particularly fresh water, clays in the formations may swell and/or disperse with attendant loss of permeability and/or mechanical strength to interfere with recovery of petroleum or other minerals from the formations. Swelling and dispersion occur when aqueous fluids used in oil recovery come in contact with the clays. Clayey formations are often impermeable or have low permeability or lose part or all of their permeability on contact of the clays with water or water base systems such as injection fluids, drilling muds, stimulation fluids and gels. Dispersed clays may also invade a permeable producing formation during drilling to create low permeability zone in the vicinity of the borehole.
Given the importance and the ubiquity of clayey or shaley formations, it is not surprising that much effort has been put into developing and improving additives for clay or shale inhibition. Various methods and additives can be found for example in the U.S. Pat. Nos. 5,342,530, 5,211,250, 5,197,544, 5,152,906, 5,099,923, 5,097,904, 5,089,151, 4,842,073, 4,830,765, 4,828,726, 4,563,292, 4,536,303, 4,536,304, 4,536,305, 4,505,833, 4,497,596, 4,172,800 and 3,578,781.
These additives usually are salts and/or polymers which effectively prevent the water from permeating the clay.
Furthermore, it is known to consolidate sandstone and other highly porous and weak formations with a fluid containing polymerizable materials, such as resins or isocyanates in combination with diols. Those methods are described for example in the U.S. Pat. Nos. 5,242,021, 5,201,612, 4,965,292, 4,761,099, 4,715,746, 4,703,800, 4,137,971, or 3,941,191. It is however important to note that the permeability of sandstones and similar formations differ from those of shale formations by several orders of magnitude. The consolidation of highly porous, unstable sandy formations and shale formations with a very low porosity are therefore generally recognized in the art as separate technical fields.
In technical fields unrelated to the present invention, efforts to form composites of clayey materials have been described. The known methods of forming so-called xe2x80x9cnanocompositesxe2x80x9d include the is addition of a reactive (monomeric or polymeric) species to clays which have been previously treated with another compound with which it will react. The ensuing chemical reaction can occur in one of two ways: either the second additive is capable of physically cross-linking the polymer, or it promotes further self-polymerization. Such processes can result in nanocomposite silicate-polymers which attain a certain degree of stiffness, strength and barrier properties with far less ceramic content than comparable glass- or mineral-reinforced polymers. As such they are far lighter in weight than conventionally filled polymers. Examples are provided by the following references: xe2x80x98Polyamide-Organoclay Compositesxe2x80x99, S. Fujiwara and T. Sakamota, Japan, Patent 51 109,998, 1976; xe2x80x98Composite Material Containing a Layered Silicatexe2x80x99, A. Usaki et al, Toyota, U.S., U.S. Pat. No. 4,889,885, (1989); M. S. Wang and T. J. Pinnavaia, xe2x80x98Clay-Polymer Nanocomposites Formed from Acidic Derivatives of Montmorillonite and an Epoxy Resinxe2x80x99, Chem. Mater., 6, 468, (1994); T. J. Pinnavaia et al, xe2x80x98On the Nature of Polyimide-Clay Hybrid Compositesxe2x80x99, Chem. Mater., 6, 573, (1994); P. B. Messersmith and E. P. Giannelis, xe2x80x98Synthesis and Characterization of Layered Silicate-Epoxy Nanocomposites,xe2x80x99 Chem. Mater., 6, 1719, (1994); T. Lan and T. J. Pinnavaia, xe2x80x98Clay-Reinforced Epoxy Nanocomposites, Chem. Mater., 6, 2216, (1994); E. P. Giannelis, xe2x80x98Polymer Layered Silicate Nanocompositesxe2x80x99, Adv. Mater., 8, 29, (1996); T. J. Pinnavaia et al, xe2x80x98Epoxy Self-Polymerization in Smectite Claysxe2x80x99, J. Phys. Chem. Solids, 57, 1005, 1996. In spite of the stabilization and strengthening that these additives impart to the resultant nanocomposite materials, there are currently several limitations to this technology which are important from an oilfield perspective. One is that the established methodology necessarily involves a high-temperature curing process for the chemical reactions to take place; another is that such an approach inevitably results in the production of composites in which the silicate is delaminated and randomly distributed within the polymer matrix. No technology has been developed which is capable of stabilizing clay silicates under ambient, aqueous conditions.
In view of the above, it is an object of the invention to provide a novel method of stabilizing subterranean clayey formations surrounding a borehole. It is another, more specific object of the invention to provide clay stabilizing additives for aqueous fluids used in drilling, completing and servicing boreholes under conditions appropriate to drilling oil wells.
This invention is concerned with the identification of a wide range of compounds which are capable of strengthening and stabilizing clay and shale minerals through a process of in-situ polymerization. These diverse compounds (or xe2x80x9cadditivesxe2x80x9d) include both monomers and polymers, in aqueous solution or suspension. The resulting nanocomposite materials, which have dramatically enhanced mechanical properties compared with the original clay and shale samples, have a vast range of potential materials-science and materials-technology applications both within and outside the oilfield.
In chemical terms, the invention comprises a wide variety of additives which are capable of stabilizing clay films in aqueous solution. The additives that have been tested encompass four broad areas: (1) species which are capable of intercalating clay galleries and affording stabilization such as diamines, polyethylene glycols (PEGs), polypropylene glycols (PPGs) and polymeric diamines; (2) reagents which are capable of undergoing condensation reactions and thus polymerizing in-situ such as diamines, aldehydes, ketones, dicarboxylic acids; (3) reagents which are capable of ring opening of epoxides or acrylates effecting polymerization in-situ such as alcohols, amines; (4) reagents which are capable of self-polymerization within clay galleries such as alkenes. All of these techniques provide considerable stabilization over untreated films.
There are three main applications of the invention. Firstly, it is envisaged that a drilling mud formulation containing a combination of the specified compounds described below may be used as a clay and shale swelling inhibitor fluid, to maintain the integrity of the wellbore during conventional drilling operations. Secondly, a completion fluid formulation containing a combination of the same compounds may be used for general remedial operations in the wellbore. Finally, the invention may be used to achieve the goal of xe2x80x9ccasingless drillingxe2x80x9d, that is to achieve with one and the same drilling and completion fluid the equivalent result of what is today obtained through a combination of drilling, casing and cementing operations.
These and other features of the invention, preferred embodiments and variants thereof, and further advantages of the invention will become appreciated and understood by those skilled in the art from the detailed description following below.